The Pathology Core will play a key role in the San Antonio Nathan Shock Aging Center because pathology increases exponentially with advancing age and is largely responsible for age-related morbidity and mortality. Knowledge of the pathological lesions associated with interventions that the Center will use to study aging is essential to interpreting the impact of these interventions on the aging process(es). This knowledge will also provide insight into the underlying mechanism(s) of the interventions. The pathological assessment of old animals is important when determining whether the changes observed as animals age are associated with or independent of underlying pathological conditions. It is, therefore, essential to obtain accurate and thorough pathological assessments of aging animals. The Pathology Core described herein will build on the extensive experience of researchers at San Antonio and the expertise of the Core Leader in rodent pathology analyses. The Specific Aims of the Pathology Core are as follows: 1 2. To conduct comprehensive end-of-life and cross-sectional pathological analyses of established and new rodent models, and other species used in aging research that die spontaneously in the aging colonies maintained in the Aging Animal and Longevity Assessment Core. To conduct quantitative morphometric analyses of the tissues/organs of transgenic rodents and their control littermates examined by the 3D and 2D image analyses. To develop a comprehensive database of histopathologic findings as a resource for trend analyses by bioinformatics personnel, to provide basic pathological information for new investigations, and to develop a tissue archive by collecting and storing tissue samples to provide a resource for the analysis of samples by special request and for new morphological research. To assist faculty and students who are interested in conducting basic biological animal research in aging with the pathological analyses needed for grant applications and manuscripts preparation.